In vivo demonstration of the Haldane effect during extracorporeal gas exchange

During the extracorporeal support (LFPPV-ECCO2R) of 11 patients suffering from severe lung failure (ARDS), we consistently noticed a higher arterial than mixed-venous PCO2 in blood samples drawn at the same time. Two explanations are possible: a) the Haldane effect (HE), b) CO2 from lung tissue metabolism. In order to distinguish changes in PCO2 due to the HE from those due to tissue CO2 production, CO2 content (CCO2) was calculated. The results were compared to animal experiments with hyperoxic apnea, after which arterial and mixed-venous samples were drawn simultaneously. All blood gas samples were analyzed for pH, PCO2, PO2, and O2-saturation, from which CCO2 was calculated. In both groups, PaCO2 was 2.15 mmHg (2.7 mmHg respectively) higher at a lower CaCO2 (-2.87 ml/l, -14.9 ml/l). Oxygen saturation increased by 8.1% in the human group and 17.8% in the animal group. A significant relationship was found between changes in PCO2 and changes in O2-saturation. This is a demonstration of the Haldane effect.